Solar cells are generally made of semiconductor materials, such as silicon (Si), which convert sunlight into useful electrical energy. A solar cell contact is in generally made of thin wafers of Si in which the required pn junction is formed by diffusing phosphorus (P) from a suitable phosphorus source into a p-type Si wafer (for example boron doped Silicon wafer) to form n-type region. The side of the silicon wafer on which sunlight is incident (n-side) is generally coated with an anti-reflective coating (ARC) to prevent reflective loss of sunlight. This ARC increases the solar cell efficiency. A two dimensional electrode grid pattern known as a front contact makes a connection to the n-side of silicon, and a coating of predominantly aluminum (Al) makes connection to the p-side of the silicon (back contact). Further, contacts known as silver rear contacts, made out of silver or silver-aluminum paste are printed and fired on the p-side of silicon to enable soldering of tabs that electrically connect one cell to the next in a solar cell module. These contacts are the electrical outlets from the pn junction to the outside load.
The additives described in this invention react with Al to form reliable and high efficiency back contacts. The reactions between additives and Al results in an earlier onset of removal of the thin surface oxide layer on Al particulates. The Al pastes containing the additives described hereinbelow offers a wider processing window and higher electrical performance.